A substrate isolation design includes a p substrate, a p well positioned on the p substrate, at least a device positioned in the p well, and at least a p substrate guard ring surrounding the device. A p+ guard ring, an n well guard ring, or a deep n well guard ring can be selectively interposed between the p substrate guard ring and the device to facilitate blocking substrate coupling effect.
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13. A substrate isolation design, comprising:
a p substrate;
at least a device positioned in the substrate;
at least a p substrate guard ring surrounding the device; and
an n well guard ring positioned between the device and the p substrate guard ring,
wherein the p substrate guard ring is positioned beneath a shallow isolation trench.
1. A substrate isolation design, comprising:
a p substrate;
a p well positioned on the substrate;
at least a device positioned in the p well;
at least a p substrate guard ring surrounding the device; and
an n well guard ring positioned between the device and the p substrate guard ring,
wherein the p substrate guard ring is positioned beneath a shallow isolation trench formed within the p well.
9. A substrate isolation design, comprising:
a substrate;
at least a device positioned on the substrate;
a first guard ring surrounding the device;
a second guard ring surrounding the first guard ring; and
a third guard ring surrounding the second guard ring, the third guard ring being a substrate guard ring, wherein the second guard ring comprises an n well guard ring and the substrate guard ring is positioned beneath a shallow isolation trench.
2. The substrate isolation design of
3. The substrate isolation design of
4. The substrate isolation design of
5. The substrate isolation design of
7. The substrate isolation design of
8. The substrate isolation design of
10. The substrate isolation design of
11. The substrate isolation design of
12. The substrate isolation design of
14. The substrate isolation design of
15. The substrate isolation design of
16. The substrate isolation design of
17. The substrate isolation design of
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1. Field of the Invention
The present invention relates to a substrate isolation design, and more particularly, to a substrate noise isolation design for isolating a P+ receiver from a P+ noise source.
2. Description of the Prior Art
Continuous scaling of CMOS technology has resulted in chips operating at ever-higher frequencies with analog and digital circuits residing in the same chip at ever-closer distances under realization of SOC (System On a Chip). Substrate noise coupling is an effect that no longer be ignored for SOC implementation involving circuit blocks that operate at frequencies near or above GHz level. The noise coupling via the substrate will impact the normal functioning of mixed-signal/RF circuits or digital circuits. The substrate noise can couple into signal through metal routing, device junction, or substrate. The major factors that affect the strength of this coupling are the frequency of operation, the separation distances between the circuit blocks, and the isolation schemes.
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The isolation structure 18 is formed on the surface of the P well 12 and interposed between the receiver 14 and the noise source 16, however, it is not effective in suppressing the substrate coupling effect particularly in high-frequency circuits. Industry has proposed or attempted to overcome this limitation with use of a guard ring formed around the receiver 14. A conventional guard ring is often formed by selectively placing certain dopants around the receiver 14, such as a P+ guard ring or an N well guard ring. In order to increase the reliability of the substrate isolation, multiple guard rings may be interposed between the receiver 14 and the noise source 16. Since extra photolithographic masking steps and critical mask alignment steps are required to form these guard rings, and each of which adds manufacturing time and expense as well as provides possible sources of device defects, it is desirable to provide an ideal substrate isolation design without adding masking steps.
It is therefore an object of the claimed invention to provide a substrate isolation design to solve the above-mentioned problems.
According to the claimed invention, the substrate isolation design includes a P substrate, a P well positioned on the P substrate, at least a device positioned in the P well, and at least a P substrate guard ring surrounding the device.
In an alternative embodiment, a P+ guard ring, an N well guard ring, or a deep N well guard ring can be selectively interposed between the P substrate guard ring and the device to facilitate blocking substrate coupling effect and improve the reliability of the substrate isolation design.
It is an advantage of the present invention that the P substrate guard ring is provided to isolate the device from other noise sources by using standard process flow of forming the device without adding extra masks. Therefore, problems such as increasing manufacturing time, steps, expense, and alignment mistakes as happened in the prior art method of forming an extra guard ring can be prevented.
These and other objects of the claimed invention will be apparent to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
Please refer to
In a better embodiment of the present invention, the first guard ring 26 (the most inner guard ring) is a P+ guard ring 26 formed by doping the portion of the P well 30 between the isolation structures 24a and 24b. The second guard ring 28 is an N well guard ring formed by doping the portion of the substrate 20 between the isolation structures 24b and 24c. The third guard ring 20a (the outer guard ring) is a P substrate guard ring positioned beneath the isolation structure 24c and between the N well guard ring 28 and the P well 30. The P substrate guard ring 20a is a portion of the P substrate 20, and an extra doping process for forming the P substrate guard ring 20a is therefore unnecessary.
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There are still other embodiments of combining any of the P+ guard ring, the N well guard ring, the deep N well guard ring or other guard rings together with the P substrate guard ring according to the present invention to provide better substrate isolation. For example, the P+guard ring can be omitted and the N well guard ring can be selectively interposed between the P substrate guard ring and the receiver/noise source to facilitate blocking substrate coupling effect and improve the reliability of the substrate isolation design.
In contrast to the prior art, the present invention utilizes the substrate to provide a substrate guard ring to improve the reliability of the substrate isolation. Since the substrate guard ring is a portion of the substrate, it is not required to add an extra doping process for forming the substrate guard ring according to the present invention.
Those skilled in the art will readily observe that numerous modifications and alterations of the design may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
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